Hello Dave, I THINK that they all had alloy bodies and door sections. By “manifold” I mean the bit on the back where all the oil distribution pipes attach.
Every one that I have seen has got ‘SMC Co Ltd’ on the outer casing, but upside down ! Also if you remove the bezel from the dial, you should find a serial number, scratched by hand, on the face of the dial. You might even be able to see it without removing the bezel and the face, but most of the celluloid faces have gone very yellow by now.